It is known to use heat-transfer fluids in refrigeration or heating systems, in particular in heat exchangers in industrial plants, such as those of nuclear power stations or solar energy converters.
Heat-transfer fluids generally consist of liquid chemical compounds or mixtures of these compounds, such as ethylene glycol, propylene glycol, petroleum-based oils, or silicones. Mention may also be made of mixtures of heavy polyaromatic compounds, aryl ethers, and terphenyls, which are particularly resistant to high temperatures and allow operation up to about 300° C. It is also known to use certain organic molten salts containing particulate additives as heat-transfer fluid. Such materials can be used over a wide temperature range, and the purpose of the particulate additives is to improve the thermal conductivity. The fluids are generally made to circulate by mechanical systems, comprising moving parts, especially blades and pumps. These mechanical systems undergo wear owing in particular to the friction caused by the passage of the heat-transfer fluid. Furthermore, when they are used at temperatures above about 350° C., these fluids undergo extensive rapid degradation and cause vapor pressure problems. Their use in the field of high-power high-temperature heat exchangers for example is therefore excluded.